Microstructure And Properties Of Al-Based Composite Coatings Prepared By Laser Cladding Under High Frequency And Light Vibration

Second generation Nickel-Based single crystal alloy CMSX-4,with high comprehensive mechanical properties and structural stability,is the first structural material for manufacturing aeroengine turbine blades.Transient liquid phase?TLP?bonding,which combines the advantages of solid diffusion bonding and high temperature brazing,is an effective welding technology to realize the connection of nickel-based single crystal alloy.,In this paper,the microstructure evolution behavior of single crystal brazed joint under different technological conditions is studied by the combination of experiment and first-principles technique.The difficulty of forming boride brittle phase in the middle layer is explored by means of theoretical calculation,and the relationship between mechanical properties and electronic structure of boride is revealed;In addition,the occupation tendency of the refractory elements?Mo,W,Ta,Re?in the single crystal structure is discussed,and the mechanism of the diffusion behavior of the refractory elements?Mo,W,Ta,Re?is revealed.The results show that:?1?The effect of different process conditions on the microstructure evolution of single crystal brazed joint was studied.The results show that at the brazing temperature of1180?,and the brazing time from 30 to120 min,the non-isothermal solidification zone,isothermal solidification zone and diffusion effected zone of single crystal brazed joint change to non-isothermal solidification zone disappear,the width of isothermal solidification zone increases,the width of diffusion effected zone increases,and the boride morphology shows in turn granular,agglomerated and acicular.?2?The structural stability,mechanical properties and electronic structure of Mn Bm?M=Ni,Cr,Mo,W,n=23,5,3,1,m=6,3,2,1?binary borides in the joint are calculated by the first principle.The results show that there is a linear relationship between the thermodynamic stability of binary borides and the boron content x:Nin Bm is?H_f=-22.21x-19.80,Crn Bm is?H_f=-151.35x+12.67,Mon Bm is?H_f=-138.60x+10.34,Wn Bm is?H_f=-100.02x+6.11.The results of mechanical properties show that Mn Bm?M=Cr,Mo,W?gradually changes from plasticity to brittleness with the increase of B content,while Nin Bm has no effect;M₅B₃ and M₃B₂ have obvious anisotropy,M₃B and MB have certain anisotropy,and M₂₃B₆ has strong isotropic characteristics;The hardness of Crn Bm is the highest,Mon Bm and Wn Bm are similar,and Nin Bm is the lowest.It is found that the pseudogap between the two peaks of strong M-B bond and Fermi energy has an important effect on the hardness and phase stability of borides.?3?The first principle method was used to study the alloying occupation of the refractory elements?Mo,W,Ta,re?and the B element in the?-Ni solid solution and??-Ni₃Al strengthening phase,and the mechanism of the effect of the refractory elements on the diffusion of the B element.The results show that the element B tends to occupy the octahedral gap of the?-Ni solid solution and the??-Ni₃Al strengthening phase.In the strengthening phase of??-Ni₃Al,the refractory element M?Mo,Ta,W,re?tends to occupy the supercell of?-Ni3Al with Ni as the center.The calculation of diffusion energy barrier shows that the energy barriers of the refractory elements m?Mo,Ta,W,Re?occupying?-Ni or??-Ni₃Al to the elements B are:3.173 and 3.347,4.007 and 4.133,3.462 and 3.701,3.211 and 2.30641ev,respectively,and the blocking order is:Ta>W>Mo>Re.The electronic structure analysis shows that the main reason for the difference of diffusion energy barrier is the difference of radius of refractory elements and the degree of 2p3d hybridization of M and B atoms.